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Their product testing usually involves several types of coal. The grind of the coal creates different shapes or fragments that vary by region, Parsons explained. The shapes can be flat slabs or pyramids, and each presents a different set of problems for the screen deck. "The flat particle will pass a long slender slot, while the pyramid shapes can get caught in the aperture like lit- tle pegs, so each has to be handled differently. The best way to identify these issues is through a good screening analysis," Parsons said. Another new screen media that the company has developed that also features molded surface features is the VST screen panel. This design incorporates slots at opposing 45˚ angles ,creating a zig-zag flow which should yield a higher retention time and allow more time to drain. "Sometimes the material flow is so rapid, the aperture is not recognized. Unless the ener- gy can be slowed, water will carry through the process," Parsons said. "The material washes off the end instead of falling through the holes. By enhancing the retention time with the VST panel, the material can find the holes, and the slower flow gives the liq- uid an opportunity to dissipate." An important aspect of the screening process that often gets ignored is the scalping stage. To work properly, a scalping screen has to be able to manage a product that's had a fairly substantial amount of water added to it. The water and dust suppression additives applied through spray nozzles and mis- ters underground raise the inherent moisture on the raw feed, creating a dilemma for the plant. "The mine adds just the right amount of moisture to this mix of coal, rock and clay to create a mixture that is one of the most difficult to screen," Parsons said. "Operators can literally grab handfuls of the raw feed and form mud balls out of it. When it dries, it can become as hard as concrete, and in cold weather, there may be enough water in the mixture to cause rapid freez- ing. Polydeck has developed a version of its Armadex bolt-down rubber product known as Armaflex to deal specifically with this issue. These screen sections use a flexible rubber and custom steel backing that provides a tremendous amount of secondary movement." In addition to the vibratory motion created by the screening machine, the secondary flexing motion created by the panel releases raw material from the media. "The object is to keep this o p e r a t i n g i d e a s c o n t i n u e d August 2015 www.coalage.com 45 ^ƉĞĐŝĂůŝnjĞĚ^ƚĞĞů^ŽůƵƟŽŶƐĨŽƌƚŚĞ DŝŶŝŶŐΘZĞĐLJĐůŝŶŐ/ŶĚƵƐƚƌŝĞƐ Toll-free: 1.866.587.6970 /ŶƚĞƌŶĂƟŽŶĂů^ĂůĞƐϮϬϱϱϰϱϱϬ ŵĂŝŶƐĂůĞƐΛĂƐƚƌĂůůŽLJĐŽŵ www.astralloy.com ƐƚƌĂůůŽLJ^ƚĞĞůWƌŽĚƵĐƚƐŝƐĂǁŚŽůůLJŽǁŶĞĚƐƵďƐŝĚŝĂƌLJŽĨEƵĐŽƌŽƌƉŽƌĂƟŽŶ the largest producer of steel in the United States. &ŽƌŶĞĂƌůLJϱϬLJĞĂƌƐƐƚƌĂůůŽLJ^ƚĞĞůWƌŽĚƵĐƚƐŚĂƐďĞĞŶƉƌŽǀŝĚŝŶŐ ŝŶŶŽǀĂƟǀĞĂŶĚĐŽƐƚĞīĞĐƟǀĞǁĞĂƌŝŵƉĂĐƚĂŶĚĂďƌĂƐŝŽŶ ƌĞƐŝƐƚĂŶƚƐƚĞĞůƐŽůƵƟŽŶƐ Specialized Plate ƐƚƌĂůůŽLJ•sΠ ƐƚƌĂůůŽLJϬϬϬΠ ƐƚƌĂůůŽLJϰϬϬΠ •ϰϱϬΠ dƌŝƉ•>•dƵīΠ ZŽů•DĂŶΠ Alloy Plate ƐƚƌĂtĞĂƌϱϱϬ ƐƚƌĂtĞĂƌϱϬϬ& ƐƚƌĂtĞĂƌϰϱϬ& ƐƚƌĂtĞĂƌϰϬϬ& •ϱϭϰ Round Alloy Bar ƐƚƌĂůůŽLJ•sΠZŽƵŶĚĂƌ ϰϯϯϬs•DŽĚZŽƵŶĚĂƌ ϰϭϰϱ,•DŽĚZŽƵŶĚĂƌ tĞŽīĞƌƐƵƉĞƌŝŽƌĐƵƐƚŽŵĞƌƐĞƌǀŝĐĞǁŝƚŚƌĞĂĚŝůLJĂǀĂŝůĂďůĞ ŝŶǀĞŶƚŽƌLJŽĨƉƌŽƉƌŝĞƚĂƌLJĂŶĚƋƵĞŶĐŚĞĚĂŶĚƚĞŵƉĞƌĞĚ ƐƚĞĞůŐƌĂĚĞƐ The cutter panels have been designed specifically for heavy-media applications.